A Structural and Magnetic Study of the Series of Double Perovskites Ca2Fe1+xW1-xO6

MARÍA RETUERTO; JOSÉ ANTONIO ALONSO; MARÍA JESÚS MARTÍNEZ-LOPE; MAR GARCÍA-HERNÁNDEZ; CARLOS A. LÓPEZ; MARÍA DEL CARMEN VIOLA; JOSÉ C. PEDREGOSA; MARÍA TERESA FERNÁNDEZ-DÍAZ

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY

WILEY-V C H VERLAG GMBH

Lugar: Weinheim; Año: 2009 vol. 25 p. 3750 - 3757

1434-1948

The synthesis of the Ca2Fe1+xW1?xO6 perovskite solid solution in the range x = 0.13?0.33 by a soft-chemistry procedure followed by annealing at different temperatures under different reducing atmospheres, and its characterization by X-ray and neutron diffraction together with magnetic measurements, is reported. The average Fe oxidation state in this series varies smoothly from Fe2.46+ in Ca2Fe1.13W0.87O6 to Fe3+ in Ca2Fe1.33W0.67O6. A detailed description of the crystal structure of four selected members of this series (x = 0.2, 0.23, 0.30, 0.33) is provided. All these compounds crystallize in the space group P21/n, with a ≈ b ≈ √2a0 and c ≈ 2a0, although they show different levels of long-range ordering between the two different cations placed at the B positions of the A2B′B″O6 perovskite structure. The driving force for this B′/B″ ordering is the charge difference between both kinds of cations, whereby the earlier members of the series, which contain a large proportion of Fe2+, are fully ordered whereas a strong antisite disorder effect is observed for the later members. The evolution of this antisite disordering has a dramatic influence on the magnetic properties across the series. Thus, for x = 0.20, the ferrimagnetic Curie temperature is above 400 K, although the saturation magnetization is very low, since there is a poor coherence between the antiferromagnetic patches formed by Fe?O?Fe interactions between the B′ and B″ positions of the perovskite, whereas the x = 0.33 compound, which has a lower TC of 310 K, shows a considerable saturation magnetization and a surprisingly strong magnetic neutron scattering for such a structurally disordered sample. The observed scattering can be ascribed to the good coherence obtained via Fe?O?Fe superexchange interactions among the Fe-rich, antiferromagnetically ordered patches that occur naturally thorughout the crystal.